Tightening PRRS Controls

Improved biosecurity practices, plus targeted vaccination strategies, can help lessen the risk of a PRRS break.

If you are serious about staying ahead of porcine reproductive and respiratory syndrome (PRRS) virus, then it’s time to tighten biosecurity measures and take aggressive steps to protect your operation from the virus.

That’s the message from Cameron Schmitt, DVM, Pipestone Vet Clinic of Iowa, based at Independence.

If you are serious about staying ahead of porcine reproductive and respiratory syndrome (PRRS) virus, then it’s time to tighten biosecurity measures and take aggressive steps to protect your operation from the virus.

That’s the message from Cameron Schmitt, DVM, Pipestone Vet Clinic of Iowa, based at Independence.

Better Biosecurity

It’s time to stop cutting corners in order to squeeze out a little savings in time and money, Schmitt says. Nine times out of 10, producers can take that approach and successfully dodge the disease. But that one time out of 10 where things go wrong can cost you a couple of million dollars in the form of a PRRS break, he warns attendees at the Iowa Pork Congress in late January in Des Moines, IA.

Instead, producers should strictly adhere to standard downtime and sanitation procedures. Provide isolation/quarantine space for breeding herds. Test stock at placement and two weeks post-placement using oral fluids or serum.

Maintain all-in, all-out production in wean-to-finish sites because continuous-flow systems tend to circulate PRRS virus and other diseases once pigs become infected.

Boar semen remains a risk, making it critical to work with reputable sources and understand their testing protocols, according to Schmitt. Don’t use semen until tests clear a batch of semen on collection day.

Sanitation must include spraying down all inanimate objects that enter the farm. Spray fomites and let dry a minimum of one hour prior to use.

Transport is highly correlated with most disease movement, Schmitt says. Trucks, trailers and truck washes need to be audited regularly. “The record on hog transport biosecurity is abysmal. I would tell you that about 80% of these auditing inspections fail. This is an area that from an industry standpoint we need to reevaluate the cost and value on transport biosecurity.”

Manure is also a concern for pathogen spread. Pigs shed PRRS virus in feces for seven days, he notes. The virus survives in slurry for 14 days at 40°F and for five days at 50-60°F. Virus survival in solids is less than 14 days in standard manure pits. PRRS becomes aerosolized during pit agitation if the pigs are shedding virus. Schmitt says the virus has been found at least 100 ft. from applicators during manure application. Pumping equipment can be fomites for virus transmission.

Air filtration systems provide added protection but are not perfect, he notes. Filter bypass or unfiltered air can gain access into your barns via gaps around filters and concrete, an open door and drains, and back-draft through unused fans.

“There have been many filtered farm PRRS breaks, so we have got to sharpen our pencils to determine if filtration is cost-effective,” Schmitt observes. “Our data indicates that we have seen about a 61% reduction in the frequency of PRRS infections on filtered farms.”

Filtering has definitely reduced PRRS infections in an area, but whether it is cost-effective will become clearer as more data is collected and analyzed, he adds.

On filtered farms in the Pipestone System, the hands and footwear of all people entering sites are swabbed. These swab samples are stored in the office for 60 days.

The samples are labeled and stored in a small freezer located in the entryway of farms. If and when a farm breaks with PRRS, those samples are analyzed to determine if the virus was carried onto the farm by workers or was blown in through the air. So far, no workers have been implicated in any breaks.

Pipestone Vet Clinic’s research committee conducted a trial of a wean-to-finish site to determine if vaccination could lower viral shedding and help reduce the chances of a nearby sow farm becoming infected. In the study, a 1,000-head room was infected with PRRS field virus as a control group, while an adjacent 1,000-head room was infected with PRRS virus and then vaccinated one week later with Boehringer Ingelheim Vetmedica’s (BIVI) PRRS ATP vaccine.

Results showed the number of PRRS virus “positive air days” outside the barn was 31 for the control group, while the vaccinated group was reduced to 17 positive air days. As well, the duration of PRRS virus shedding was reduced from 70 days for the control group of pigs to 45 days for the vaccinated group, Schmitt says.

Pipestone’s research committee recently completed a second vaccine trial with the same BIVI vaccine. Using the same experimental design, vaccination of wean-to-finish pigs following infection with a field strain of PRRS virus limited viral shedding to just five days in air outside the barn.

“We have dramatically reduced the risk to that neighboring sow farm when a nearby wean-to-finish site breaks, providing another tool in our toolkit,” Schmitt says.

The goal of a project conducted by the Pipestone group last March (2012) was to determine the frequency in which farms are challenged by PRRS virus in air outside filtered sow farms vs. air outside PRRS-positive farms. Air was sampled outside exhaust fans.

“The frequency in which positive air samples were detected was pretty impressive,” Schmitt says. Not surprisingly, the source farm recorded 75% frequency of virus detected. The four recipient farms had 64%, 41%, 65% and 0% frequency of virus detected. Historically, virus frequency has been detected on just 3-11% of farms tested.

Sow Studies

A study by a University of Minnesota research team, presented at last fall’s Leman Swine Conference in St. Paul, MN, sought to establish the best way to run a sow farm to avoid PRRS.

Researchers looked at two basic parameters in analyzing 61 PRRS breaks in sow farms: the length of time it took from a PRRS break to produce negative pigs, and the length of time it took from a PRRS break to return to baseline production or productivity prior to the break. The study compared the value of live virus inoculation (LVI) vs. the use of vaccine.

“What they found was that if a producer wanted negative pigs more quickly, the use of LVI produced negative pigs more quickly, between 6-9 weeks sooner after a break,” Schmitt explains.

“But you get back to baseline production more quickly and net total losses of pigs are lower when vaccine is used in a PRRS break,” he clarifies.

A third parameter examined whether a sow herd was better off being PRRS positive or negative prior to a break. “Being positive to PRRS previously resulted more quickly in the production of negative pigs,” Schmitt states.

When comparing the economics of strategies to clean up a sow farm after a break, it is more economical to use vaccine to get back to baseline production more quickly and maintain throughput in the wean-to-finish flow, he says.

Breaks like Clockwork

Based on four years of statistical data from 11 participating production systems across the Midwest, herds start breaking with PRRS like clockwork between Oct. 13 and Oct. 19 every year.

“Last year, we thought it was earlier because crops were out early and we started pumping manure earlier, but the data for PRRS breaks say it was during the same time period,” Schmitt says.

This information can help producers with planning pig flows and possibly with developing a standardized vaccination protocol to head off those breaks, he observes. Some groups have started a super-inoculation herd protection program, vaccinating sows on Sept. 1, then again 30 days later, to ward off the severity of those PRRS breaks.

However, more research is needed to validate those approaches, Schmitt says. “The industry needs to utilize proven scientific knowledge, not just what might work or seems to work.”